One source of error is refraction, the bending of light beams as they pass through air layers of different temperature and pressure.

误差的一个来源是折射，即光束通过不同温度和压力的空气层时发生的弯曲现象。

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A recent survey by China Youth Daily found that jobs are the major source of pressure for about 60 percent of college students.

最近，《中国青年报》的一项调查显示，约60%大学生表示压力主要来源于工作。

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One doctor claims that sleep bruxism results in 250 lbs. of pressure on the tooth [source: NY Times].

一个医生声称睡觉时磨牙能施加250磅的压力到牙齿上。

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It is even more difficult when trying to put pressure on the source of the problem.

ECONOMIST: Europe.view

The best source of pressure is the knowledge that there may never be a better chance than now.

ECONOMIST: Cyprus, Turkey and the European Union

Nor is legislation the only source of pressure.

ECONOMIST: History in California